Superconducting device

ABSTRACT

Superconducting device include a type having a structure of a superconductor--a normal-conductor (or a semiconductor)--a superconductor, and a type having a superconducting weak-link portion between superconductors. 
     The superconductors constituting the superconducting device are made of an oxide of either of perovskite type and K 2  NiF 4  type crystalline structures, containing at least one element selected from the group consisting of Ba, Sr, Ca, Mg, and Ra; at least one element selected from the group consisting of La, Y, Ce, Sc, Sm, Eu, Er, Gd, Ho, Yb, Nd, Pr, Lu, and Tb; Cu; and O. In addition, the c-axis of the crystal of the superconductor is substantially perpendicular to the direction of current flowing through this superconductor.

This is a continuation of application Ser. No. 08/462,356, filed Jun. 5,1995 (now U.S. Pat. No. 5,729,046); which is a divisional of applicationSer. No. 08/192,573 filed Feb. 7, 1994 (now U.S. Pat No. 5,552,375);which is a continuation of application Ser. No. 07/853,593 filed Mar.17, 1992 (now U.S. Pat. No. 5,326,745); which is a division ofapplication Ser. No. 07/155,806 filed Feb. 16, 1988 (now U.S. Pat No.5,126,315).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a superconducting device which operatesat the liquid nitrogen temperature or above, and more particularly to asuperconducting device which is readily produced and which operatesstably.

2. Description of the Related Art

Heretofore, materials such as Nb₃ Ge have been used as the materials ofsuperconducting devices which operate at high temperatures. Thistechnique is discussed by H. Rogalla et al. in "IEEE Transactions,"MAG-15, 536 (1985).

A prior-art superconducting device in which a plurality of electrodesexhibitive of a superconductivity are coupled through a semiconductor ora normal-conductor, is discussed by R. B. van Dover et al. in "Journalof Applied Physics," vol. 52, p. 7327, 1981. Besides, a three-terminalsuperconducting device in which the above superconducting device isadditionally provided with means for changing the coupling between thesuperconducting electrodes on the basis of the field effect is discussedby T. D. Clark et al. in "Journal of Applied Physics," vol. 5, p. 2736,1980. The sectional structure of the three-terminal superconductingdevice is shown in FIG. 1. In this device, the value of asuperconducting current to flow via a semiconductor layer 2 across twosuperconducting electrodes 3a and 3b disposed in contact with thesemiconductor layer 2 on a substrate 1 is controlled in such a way thatthe superconducting proximity effect is changed by a voltage applied toa control electrode 5 disposed between both the electrodes 3a and 3b.The control electrode 5 is disposed on the semiconductor layer 2 throughan electric insulator film 4.

The prior art has used Pb, Pb alloys, Nb and Nb compounds as thematerials of the superconducting electrodes. In order to operate thesuperconducting device employing any of these materials, accordingly,the device must be installed in the atmosphere of a cryogenictemperature near the liquid helium temperature (4.2 K). Further, the twosuperconducting electrodes must be provided at a spacing within 0.5 μmin order to intensify the influence of the superconducting proximityeffect between these superconducting electrodes, and this has made thefabrication of the device very difficult.

Moreover, in the prior art, the suderconducting electrodes and thesemiconductor or normal-conductor have been made of different materialsof elements. By way of example, the material of the superconductingelectrodes has been any of Nb, Pb alloys, Sn etc., while the material ofthe semiconductor or normal-conductor has been any of Si, InAs, Cu, etc.The combination of these materials, however, signifies that the deviceis constructed by stacking the materials of the superconductors and thesemiconductor or normal-conductor, the electrical properties of whichare quite different. That is, the superconducting device has a structurein which the surface of the semiconductor or normal-conductor isoverlaid with the superconductors made of the different material. Onthis occasion, the characteristics of the superconductors are highlysusceptible to the state of the surface of the semiconductor ornormal-conductor, so that the characteristics of the device of such astructure are liable to change. It has therefore been difficult toreproducibly fabricate the superconducting device of this type.

The superconducting critical temperature (T_(c)) of the superconductorsis at most 10-20 K or so. This signifies that the characteristics of thedevice are prone to become unstable due to the temperature changethereof.

Since the prior-art superconducting device operates chiefly at theliquid helium temperature, it has been cooled down to that temperatureby a method of immersion in liquid helium or cooling with helium gas.The liquid helium, however, is very expensive and is uneconomical as acoolant. Another problem has been that, since the liquid helium is atthe temperature much lower than the room temperature, the handlingthereof is, in itself, difficult. These problems of the liquid heliumhave directly led to problems on the economy and handling of thesuperconducting device itself.

In addition, the superconducting materials having heretofore been usedare polycrystalline or amorphous. With the polycrystalline material, itis difficult to precisely microfabricate a part of or less than 0.5 μm.Besides, in case of using a material whose property as a superconductordepends upon the orientation of a crystal, the degree of the crystalorientation of the crystal grain of the polycrystalline material needsto be strictly controlled each time the superconductor is fabricated. Ingeneral, however, this control is difficult and has therefore incurredthe problem that variation in characteristics at the stage ofmanufacture becomes large.

Typical as the structure of a prior-art superconducting device having asuperconducting weak-link element is the so-called "micro-bridge" inwhich a superconducting film is partially fined to form a constriction,the constricted portion being endowed with a weak link property.Especially for the Nb-type superconducting material, optical patterningtechnology or electron-beam lithography and technology for processingthe superconducting film have been combined to fabricate thesuperconducting weak-link element. Such a weak-link element is utilizedas a magnetic quantum flux detector capable of detecting a feeblemagnetic field or as a microwave/millimeter-wave detector of highsensitivity. The magnetic quantum flux detector has as high a fluxresolving power as 10⁻⁹ Oe., and is applied to a magnetoencephalogramdetector and a magnetocardiogram detector. The microwave detection rangeof the weak-link element can cover a high frequency band up to 10¹² Hzwhich cannot be attained with another semiconductor element. In thismanner, the superconducting device furnished with the superconductingweak-link element exhibits the excellent performance as the detector forthe electromagnetic waves. Since, however, the Nb-type superconductingmaterial in the prior art has a critical temperature of 23 K or below,also the superconducting device formed using the Nb-type superconductingmaterial has inevitably been operated in the liquid helium (4.2 K).

Such a known example is stated in "IEEE Transactions on Magnetics," vol.MAG-21, No. 2, MARCH 1985, pp. 932-934.

SUMMARY OF THE INVENTION

The first object of the present invention is to provide asuperconducting device which operates stably against temperature changesand which is operable at a temperature of or above the liquid nitrogentemperature.

The second object of the present invention is to provide asuperconducting device which is superior in economy and which is easy ofhandling.

The third object of the present invention is to provide asuperconducting device which can be easily manufactured and whichaffords articles of uniform characteristics.

The fourth object of the present invention is to provide asuperconducting device which affords an efficient flow ofsuperconducting electrons.

The fifth object of the present invention is to provide asuperconducting device the device sensitivity and gain of which arehigh.

The first, second, third and fourth objects mentioned above areaccomplished in such a way that the c-axis of the crystal of an oxidesuperconductor constituting the superconducting device is oriented so asto become substantially perpendicular to the direction ofsuperconducting current which flows within the oxide superconductor.

For example, in a superconducting material having a layered perovskitecrystalline structure with oxygen vacancy or a K₂ NiF₄ -type crystallinestructure, the superconducting property depends upon thecrystallographic orientation in such a manner that a superconductivitywithin a plane perpendicular to the c-axis, namely, within the c-planeis intense and that carriers behave intensely in two dimensions withinthe plane. Therefore, the direction in which a great current sufficientfor use as the device can be caused to flow lies within the c-plane, andthis plane has the flow of superconducting electrons about 10 times asmany as those in any other plane. Thus, the superconducting current canbe caused to flow efficiently by the measure that the c-axis of thecrystal of the superconductor is oriented substantially orthogonal tothe direction of the current flowing within the superconductor.

According to the present invention, in a superconducting device in whicha superconductor and a normal-conductor or semiconductor are used incombination, crystal lattices at the interface between thesuperconductor and the normal-conductor or semiconductor are formed intoa matched state, and besides, the direction in which current flowswithin the device agrees with the direction in which thesuperconductivity of the material is high, so that a sufficiently greatsuperconducting current can be caused to flow. The invention thereforehas the effect that a superconducting device which has stablecharacteristics and can be produced at favorable reproducibility andwhich affords a stable circuit operation can be realized.

The first, second, third and fifth objects mentioned above areaccomplished by connecting a superconductor and a normal-conductor (orsemiconductor) so that the c-plane of the crystal of the superconductormay become perpendicular to the contact plane of the superconductor andthe normal-conductor (or semiconductor). According to this construction,the probability at which electron pairs or electrons leak from thesuperconductor into the semiconductor or normal-conductor becomes high.That is, the interface between the superconductor and the semiconductoror normal-conductor matches well with electron waves, and an efficientflow of electrons arises. Accordingly, it becomes possible to realize asuperconducting device of stable operation and high gain. A similareffect can be attained also in case of employing a polycrystallinematerial in which crystal grains are oriented.

Further, in a superconducting material having a K₂ NiF₄ -typecrystalline structure whose composition is indicated by (La_(1-x)A_(x))₂ CuO₄ (where the letter A denotes a substance such as Sr_(1-y-z)Ba_(y) Ca_(z)), the superconducting property depends upon thecrystallographic orientation (oriented polycrystalline film) in such amanner that a superconductor exhibits an intense anisotropicelectrically-conducting characteristic within the c-plane, namely, theplane perpendicular to the c-axis. Therefore, the direction in which agreat current sufficient as a device is caused to flow needs to liewithin the plane perpendicular to the c-axis of the crystal. For thisreason, a plane where the superconductor and a normal-conductor lie incontact with a substrate to form the superconducting device thereon, inother words, the front surface of the substrate, should desirably beperpendicular to the c-axis of the single-crystal material of which thesuperconductor or the normal-conductor is made. In this case, thedirection of the current flow and the direction of the highestsuperconductivity agree in the superconducting device, so that theoperation of the device can be stabilized.

The above has referred to the case of using monocrystalline materialsfor the superconducting electrodes and the semiconductor, but a similareffect can be attained also in case of employing polycrystallinematerials in which crystal grains are oriented. Also in this case, it isdesired for the orientation of the crystal grains that the c-axes of thecrystal grains become perpendicular to the front surface of thesubstrate. On the oriented normal-conductor or semiconductor, thesuperconducting electrodes having the same orientation are readilyformed. In such a case, the same effect as in the above-stated case ofemploying the monocrystalline materials can be attained.

Besides, it has been explained above that the normal-conductor orsemiconductor is first formed and that the superconductor issubsequently formed. However, even when this order is altered, a quitesimilar effect can be brought forth.

These and other objects and many of the attendant advantages of thisinvention will be readily appreciated as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view for explaining a superconducting device in aprior art;

FIG. 2 is a sectional view showing a part of a superconducting deviceaccording to the first embodiment of the present invention;

FIG. 3 is a sectional view showing a part of a superconducting deviceaccording to the second embodiment of the present invention;

FIG. 4 is a sectional view showing a part of a superconducting deviceaccording to the third embodiment of the present invention;

FIG. 5 is a sectional view showing a part of a superconducting deviceaccording to the fourth embodiment of the present invention;

FIG. 6 is a sectional view showing a superconducting device which is thefifth embodiment of the present invention;

FIG. 7 is a sectional view showing a superconducting device which is thesixth embodiment;

FIG. 8 is a sectional view showing a part of a superconducting devicewhich is the seventh embodiment;

FIG. 9 is a sectional view showing a superconducting device which is theeighth embodiment;

FIG. 10 is a sectional view showing a part of a superconducting deviceaccording to the ninth embodiment of the present invention;

FIG. 11 is a sectional view showing the tenth embodiment of the presentinvention;

FIG. 12 is a sectional view showing the eleventh embodiment;

FIG. 13 is a sectional view showing the twelfth embodiment;

FIG. 14 is a diagram showing the atomic arrangement of a Ba--Y--Cuoxide;

FIG. 15 is a sectional view showing the thirteenth embodiment; and

FIG. 16 is a sectional view showing an embodiment in which thesuperconducting device in FIG. 15 is employed as a photodetector device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, the present invention will be described in detail in conjunctionwith embodiments.

[Embodiment 1]

The first embodiment of the present invention will be described withreference to FIG. 2. A substrate 1 is made of an SrTiO₃ single crystal,the principal surface of which is perpendicular to the c-axis thereof.On the principal surface of the substrate 1, a normal-conductor orsemiconductor 2 which has a composition of (La₀.9 Ca₀.1)₂ CuO₄ and whichis about 100 nm thick is formed by sputtering. Since thenormal-conductor or semiconductor 2 is formed on the flat substrate 1,the film thickness thereof is fixed. The normal-conductor orsemiconductor 2 is heat-treated at about 1000° C. for about 10 secondsby inductive heating. Then, it becomes a single-crystal thin film thec-axis of which lies in the same direction as the c-axis of thesubstrate 1. Subsequently, a superconductor 3 having a composition of(La₀.9 Sr₀.1)₂ CuO₄ and being about 100 nm thick is similarly formed bysputtering. Since the superconductor 3 has a crystal orientationdependent upon the orientation of the subbing normal-conductor orsemiconductor 2, it is also oriented in the c-axial direction likewiseto the substrate 1 and the normal-conductor or semiconductor 2. Apattern of photoresist is formed on the surface of the superconductor 3,whereupon using it as a mask, sputter-etching with Ar ions is carriedout to process the superconductor 3 into two opposing superconductingelectrodes 3a and 3b. The length between the two superconductingelectrodes 3a and 3b is about 3-10 times the coherence length of thenormal-conductor or semiconductor 2. Subsequently, a protective film 6made of SiO₂ and having a thickness of about 150 nm is formed bychemical vapor deposition (CVD). This protective film 6 is formed inorder to prevent the drawback that, in a case where an oxide containinga rare-earth element is used as the material of the superconductor 3,the superconducting characteristics of the material are changed by thediffusion of hydrogen or oxygen and the composition change of thesurface of the material, so the characteristics of the devicedeteriorate with time. In this manner, when the oxide-type material isapplied to the superconductor as in the present embodiment, the use ofthe protective film 6 is desirable. Apart from SiO₂, the material of theprotective film 6 may well be an electric insulator such as SiO or Si₃N₄, an organic high polymer, or the like. In the above way, thesuperconducting device having the structure of the superconductor3a--normal-conductor (semiconductor) 2--superconductor 3b can beobtained. In this case, the interface between the normal-conductor 2 andthe superconductor 3 was free from contamination, etc., because both thelayers were formed to be continuous, and it could be formed under anideal state with little reflection of carriers because crystal latticesmatched favorably. These brought forth the effects that the uniformityand reproducibility of characteristics were excellent and that circuitoperations became stable. In the present embodiment, SrTiO₃ or sapphirewas employed as the material of the substrate 1. Alternatively, aceramics material such as SiC or a garnet material such as GGG may wellbe employed.

[Embodiment 2]

Next, the second embodiment of the present invention will be describedwith reference to FIG. 3. In the first embodiment, the normal-conductoror semiconductor 2 was previously formed. As already described, however,the superconductor 3 can be previously formed. Conditions for theformation may be similar to those of the first embodiment. Morespecifically, on a substrate 1 (SrTiO₃ single crystal) the principalsurface of which is perpendicular to the c-axis of the crystal, asuperconductor 3 having a composition of (La₀.9 Sr₀.1)₂ CuO₄ and beingabout 100 nm thick is formed by sputtering. A pattern of photoresist isformed on the surface of the superconductor 3, whereupon using it as amask, the superconductor 3 is etched and processed to form two opposingsuperconducting electrodes 3a and 3b. Subsequently, a normal-conductoror semiconductor 2 having a composition of (La₀.9 Ca₀.1)₂ CuO₄ and beingabout 200 nm thick is deposited and formed by sputtering. Thisnormal-conductor or semiconductor is heat-treated at about 1000° C. forabout 10 seconds by inductive heating. Then, the normal-conductor orsemiconductor 2 and the superconductors 3 become polycrystalline orsingle-crystal thin films the c-axes of which lie in the same directionas the c-axis of the substrate 1 (in other words, in a directionperpendicular to the principal surface of the substrate 1) as inEmbodiment 1. In this way, the device of the present invention havingthe structure of the superconductor 3a--normal-conductor (semiconductor)2--superconductor 3b can be obtained.

[Embodiment 3]

Next, the third embodiment of the present invention will be describedwith reference to FIG. 4. On the surface of the superconducting deviceaccording to the first embodiment illustrated in FIG. 2, an electricinsulator film 4 made of SiO₂ and being about 20-120 nm thick is formedby CVD (chemical vapor deposition) without forming the protective film6. Subsequently, a control electrode 5 made of Nb and being about 300 nmthick is formed by deposition based on sputtering and processing basedon reactive ion etching with CF₄ gas. Thus, a three-terminalsuperconducting device can be realized. The control electrode 5 cancontrol current which flows across the two superconducting electrodes 3aand 3b. Although this device includes the control electrode 5, it can ofcourse offer the superconducting device which is excellent in theuniformity and reproducibility of characteristics, likewise to the twopreceding embodiments.

[Embodiment 4]

Now, the fourth embodiment of the present invention will be describedwith reference to FIG. 5. On a substrate 1 (SrTiO₃ single crystal orsapphire) the principal surface of which is perpendicular to the c-axisof the crystal, a superconductor 3a having a composition of (La₀.9Sr₀.1)₂ CuO₄ and being about 100 nm thick is formed by sputtering. Thissuperconductor 3a is heat-treated in an oxygen atmosphere at about 920°C. for 2 hours. Thus, it can be turned into a polycrystalline thin filmor single-crystal thin film the c-axis of which lies in the samedirection as that of the substrate 1. Subsequently, a normal-conductoror semiconductor 2 having a composition of (La₀.9 Ca₀.1)₂ CO₄ and beingabout 100 nm thick, and a second superconductor 3b having a compositionof (La₀.9 Sr₀.1)₂ CuO₄ and being about 200 nm thick are formed byion-beam sputtering.

The superconductor 3a is processed by chemical etching in which apattern of photoresist is used as a pattern. The normal-conductor orsemiconductor 2 and the second superconductor 3b are formed through ametal mask. In addition, the superconductor 3b is heat-treated in anoxygen atmosphere at about 920° C. for 2 hours. Thus, likewise to thesuperconductor 3a, this superconductor 3b turns into a polycrystallinethin film the c-axis of which lies in the same direction as that of thesubstrate 1. At the next step, a protective film 6 made of SiO₂ andhaving a thickness of about 150 nm is formed by chemical vapordeposition (CVD). In the above way, the superconducting device havingthe structure of the superconductor 3a--normal-conductor (semiconductor)2--superconductor 3b can be obtained. The present embodiment has thesandwich structure in which the superconductor 3a and the secondsuperconductor 3b hold the normal-conductor or semiconductor 2therebetween. It differs from the first embodiment of the presentinvention in this point. Even with such a sandwich structure, theobjects of the present invention can be satisfactorily achieved. In thecase where the semiconductor is sandwiched as the member 2, a Schottkybarrier intervenes between each superconductor and the semiconductor,and the tunnel effect becomes important in the mechanism of electricconduction. Needless to say, however, the present invention issufficiently effective even for such a tunnel junction.

[Embodiment 5]

The material of the superconducting electrodes employed in thesuperconducting devices disclosed as the embodiments of FIGS. 2 thru 5is the superconducting oxide material of the perovskite type having ahigh superconducting critical temperature. In this material, in view ofthe crystalline structure, superconducting electron pairs are easy offlowing in the direction of the a-b plane (in a direction perpendicularto the c-axis) and are difficult of flowing in the same direction as thec-axis. Accordingly, the superconducting current of the superconductingdevice employing such a material for the superconducting electrodesflows in the direction of the superconducting electrode3a→normal-conductor (semiconductor) 2→superconducting electrode 3b.Therefore, the flows of electrons at the interfaces between thesuperconducting electrodes 3a, 3b and the normal-conductor(semiconductor) 2 become important. That is, the flow of current fromthe superconducting electrode 3a to the normal-conductor (semiconductor)2 and the flow of current from the normal-conductor (semiconductor) 2 tothe superconducting electrode 3b must be respectively enlarged.

In the case of FIG. 3, the currents of the superconducting electrodes 3aand 3b flow in parallel with the principal surface of the substrate 1(vertically to the c-axis). Accordingly, the maximum superconductingcurrent flows across the superconducting electrodes 3a and 3b via thenormal-conductor (semiconductor) 2. In contrast, in the case where thelayer of the superconducting electrodes 3a, 3b and that of thenormal-conductor (semiconductor) 2 are different as in FIG. 2 or FIG. 4,the flow of the current from the superconducting electrode 3a to thenormal-conductor (semiconductor) 2 and that of the current from thenormal-conductor (semiconductor) 2 to the superconducting electrode 3bintersect orthogonally to the flows of the currents of thesuperconducting electrodes 3a, 3b. Accordingly, such a superconductingdevice has had the problem that a sufficient superconducting currentcannot be caused to flow across the superconductors 3a and 3b via thenormal-conductor (semiconductor) 2 in the structure of thesuperconducting electrode 3a--normal-conductor (semiconductor)2--superconducting electrode 3b.

An embodiment which has solved this problem will now be described.

FIG. 6 is a sectional view of a superconducting device which is thefifth embodiment of the resent invention. Unlike those of the first thrufourth embodiments, a substrate indicated at numeral 11 is made ofSrTiO₃ and has its principal surface oriented to be parallel to thec-axis of the crystal. On this substrate 11, a normal-conductor(semiconductor) 2 having a composition of (La₀.9 Ca₀.1)₂ CuO₄ and being200 nm thick is formed by sputtering. Thereafter, this normal-conductor(semiconductor) 2 is heat-treated at 100° C. for 10 seconds by inductiveheating. Then, it becomes a single-crystal thin film the c-axis of whichis parallel to that of the substrate 11. Subsequently, a superconductingthin film having a composition of (La₀.9 Sr₀.1)₂ CuO₄ and being about300 nm thick is formed by sputtering. Since this superconducting thinfilm has a crystal orientation dependent upon the orientation of thecrystal of the subbing normal-conductor (semiconductor) 2, it is sooriented that the c-axis thereof is parallel to the surface of thenormal-conductor (semiconductor) 2, in other words, that the c-planethereof is perpendicular to the same surface. Subsequently, thesuperconducting film is heated in an oxygen atmosphere of 950° C. for 1hour. Thereafter, a pattern of photoresist is formed on the surface ofthe superconducting thin film. Using the pattern as a mask,sputter-etching with Ar ions is carried out to form two opposingsuperconducting electrodes 3a and 3b.

At the next step, an electric insulator film 7 made of SiO₂ and having athickness of about 120 nm is formed by chemical vapor deposition (CVD).Subsequently, superconducting wiring leads 3c and 3d having thecomposition of (La0.9Sr₀.1)₂ CuO₄ and being about 100 nm thick areformed by ion-beam sputtering. Further, the superconducting wiring leads3c and 3d are heated in an oxygen atmosphere of about 950° C. for 1hour. Since the subbing material of the superconducting wiring leads 3cand 3d is the amorphous SiO₂ forming the insulator film 7, the c-axis ofthe crystal grain of the material forming these superconducting wiringleads is prone to be directed perpendicularly to the principal surfaceof the substrate 11. That is, the c-axes of the superconducting wiringleads 3c and 3d are prone to be oriented perpendicularly to theprincipal surface of the substrate 11. Although the orientation of thecrystal grains is not perfect, a greater superconducting current can becaused to flow stably by making the orientation of the superconductingelectrodes 3a, 3b and that of the superconducting wiring leads 3c, 3ddifferent in this manner.

In this way, the superconducting device having the structure of thesuperconductor 3a--semiconductor 2--superconductor 3b can be obtained.With this device, the currents of the interfaces between thesuperconductors 3a, 3b and the semiconductor 2 flow favorably, and thedirection of the flows agrees with the direction of a highsuperconductivity, so that the critical superconducting current to flowacross the superconducting electrodes 3a and 3b increases to afford astable operation.

[Embodiment 6]

Now, a superconducting device which is the sixth embodiment of thepresent invention will be described with reference to FIG. 7.

A control electrode 5 for controlling a superconducting current is addedto the superconducting device which is the embodiment in FIG. 6. In FIG.7, for the brevity of illustration, the superconducting wiring leads 3cand 3d in FIG. 6 are symbolically indicated, and the insulator film 7 isomitted from the illustration.

On the surface of the device disclosed as the fifth embodiment, anelectric insulator film 4 made of SiO₂ and having a thickness of 100 nmis deposited by chemical vapor deposition (CVD). Thereafter, an Nb filmhaving a thickness of about 300 nm is deposited by dc magnetronsputtering and is etched with CF₄ gas by employing a mask of photoresistso as to form the control electrode 5. In this way, a three-terminalsuperconducting device can be obtained. This device can enhance thesuperconducting proximity effect likewise to the fifth embodiment, andcan therefore increase the magnitude of variation of the criticalsuperconducting current relative to a fixed voltage applied to thecontrol electrode. Accordingly, the gain of the device enlarges, and astable operation is exhibited.

[Embodiment 7]

FIG. 8 is a sectional view of a superconducting device which is theseventh embodiment of the present invention. As in FIG. 1, a substrate 1is made of an SrTiO₃ single crystal the principal surface of which isperpendicular to the c-axis. On this substrate 1, a normal-conductor(semiconductor) 2 made of (La₀.9 Ca₀.1)₂ CuO₄ and having a thickness of500 nm is deposited by sputtering. Thereafter, the normal-conductor(semiconductor) 2 is heated at 1000° C. for 10 seconds by inductiveheating. The c-axis of the normal-conductor (semiconductor) 2 lies inthe same direction as the c-axis of the substrate 1, that is, it isperpendicular to the principal surface of the substrate 1. Using a maskof photoresist, the normal-conductor (semiconductor) 2 is etched down toa depth of 300 nm by plasma etching with CF₄ gas, whereby a projection2a having a width of at most 0.5 μm is provided. Subsequently, aninter-layer insulator film 7 made of SiO₂ and having a thickness of 100nm is formed by CVD. Thereafter, superconducting thin films 3a and 3bhaving a composition of (La₀.9 Sr₀.1)₂ CuO₄ and being 200 nm thick areformed by sputtering. Here, the superconducting thin films are sooriented that the c-planes thereof become perpendicular to the the sidefaces of the projection 2a made of the normal-conductor (semiconductor)2. At the subsequent step, the photoresist is removed with a solvent.Then, the superconducting device shown in FIG. 8 is obtained. Since thisdevice can enhance the superconducting proximity effect likewise to theembodiment in FIG. 2, the critical superconducting current increases,and a stable operation is exhibited.

[Embodiment 8]

FIG. 9 is a sectional view of a superconducting device which is theeighth embodiment of the present invention. This superconducting deviceis such that the device of the embodiment in FIG. 8 is additionallyprovided with a control electrode 5 for controlling a superconductingcurrent. On the surface of the device disclosed as the embodiment inFIG. 8, an electric insulator film 4 made of SiO₂ and having a thicknessof 100 nm is formed by CVD. Thereafter, an Nb film having a thickness of300 nm is formed by dc magnetron sputtering. It is processed by reactiveion etching with CF₄ gas, thereby to form the control electrode 5. Inthis way, the superconducting device shown in FIG. 9 can be obtained.According to this device, the magnitude of variation of the criticalsuperconducting current relative to a fixed voltage applied to thecontrol electrode can be increased. The gain of the device enlarges, anda stable operation is exhibited.

[Embodiment 9]

Next, the ninth embodiment of the present invention will be describedwith reference to FIG. 10. On a substrate 11 made of the single crystalof SrTiO₃, a superconductor 3 having a composition of (La₀.9 Sr₀.1)₂CuO₄ and being about 1 μm is deposited by sputtering so that the c-axisof the crystal may become perpendicular to the substrate. To this end,the crystal orientation of the principal surface of the substrate 11 maybe selected to the c-plane beforehand. Subsequently, the superconductor3 is heated in an oxygen atmosphere of 900° C. for 2 hours. Thereafter,a part of the superconductor is processed by Ar-ion etching so as toform a superconducting weak-link portion 9 which is about 0.2 μm thickand about 0.1 μm wide. At the subsequent step, a photoconductivesemiconductor 8 made of CdS is formed on the weak-link portion. Then,the superconducting device of the present invention is fabricated. Inthe above way, it is possible to realize the superconducting deviceconstructed of two superconductign electrodes 3a and 3b which areseparated by the weak-link portion 9 and the c-planes of which are inperpendicular contact with the photoconductive semiconductor 8. In thedevice having such a structure, the direction in which the maximumsuperconducting current across the superconducting electrodes 3a and 3bflows and the direction of the flows of currents along thesuperconducting electrode 3a--photoconductive semiconductor8--superconducting electrode 3b are in agreement and are the directionof an x-axis shown in the figure. Therefore, when light 10 is projectedon the phtoconductive semiconductor 8, a great current can be caused toflow. Accordingly, the value of the current to flow in the x-axialdirection can be readily controlled with the projection light of verylow intensity, and the device operates as a photodetective device ofhigh sensitivity and high speed.

[Embodiment 10]

Now, the tenth embodiment of the present invention will be describedwith reference to FIG. 11. On a photoconductive semiconductor 8 made ofCdS, a superconductor having a composition of (La₀.9 Sr0.1)₂ CuO₄ andbeing 1 μm thick is deposited by sputtering so that the c-axis of thecrystal thereof may become parallel to the substrate 8. Subsequently,the superconductor is heated in an oxygen atmosphere of 950° C. for 2hours. Thereafter, a part of the superconductor is removed by Ar-ionetching so as to form a superconducting weak-link portion 9 which is 0.2μm thick and 0.1 μm wide. Then, the superconducting device of thepresent invention is fabricated. In this device, the direction in whichthe maximum superconducting current across superconducting electrodes 3aand 3b flows agrees with the direction of the flow of current from thesuperconducting electrode 3a to the photoconductive semiconductor 8 andthe flow of current from the photoconductive semiconductor 8 to thesuperconducting electrode 3b. Therefore, when light 10 is projected onthe photoconductive semiconductor 8, a great current can be caused toflow. Accordingly, the device operates as a photodetective device ofhigh sensitivity and high speed in which the value of the current can bereadily controlled with a slight amount of current.

[Embodiment 11]

Next, the eleventh embodiment of the present invention will be describedwith reference to FIG. 12. Using a mask of photoresist, aphotoconductive semiconductor 8 made of CdS is processed by Ar-ionetching so as to form a projection which is 1 μm high and 0.1 μm wide.After the mask is removed, a superconductor having a composition of(La₀.9 Sr₀.1)₂ CuO₄ and being 2 μm thick is deposited so that the c-axisof the crystal thereof may become perpendicular to the surface of thesemiconductor 8. This superconductor is subjected to plasma etching withCF₄ gas so that the surface of the superconductor may become uniform andthat the thickness thereof on the projection may become 0.2 μm.Subsequently, the superconductor is heated in an oxygen atmosphere at950° C. for 2 hours. Then, the superconducting device of the presentinvention is fabricated.

In this device, the direction in which the maximum superconductingcurrent across superconducting electrodes 3a and 3b flows agrees withthe direction of the flows of currents along the superconductingelectrode 3a--photoconductive semiconductor 8--superconducting electrode3b. Therefore, when light 10 is projected on the photoconductivesemiconductor 8, a great current can be caused to flow. Accordingly, thevalue of the current to flow can be readily controlled with the light,and the device operates as a photodetective device of high sensitivityand high speed.

[Embodiment 12]

Next, the twelfth embodiment of the present invention will be describedwith reference to FIG. 13. On a substrate 11 made of SrTiO₃ and having asurface perpendicular to the c-axis thereof, a photoconductivesemiconductor 8 made of CdS and having a thickness of 1 μm is deposited.It is processed into a width of 0.1 μm by Ar-gas ion etching.Subsequently, a superconductor having a composition of (La₀.9 Sr₀.1)₂CuO₄ and being 2 μm thick is deposited so that the c-axis of the crystalthereof may become perpendicular to the surface of the substrate 11.This superconductor is subjected to plasma etching with CF₄ gas so thatthe surface of the superconductor may become uniform and that thethickness thereof on the photoconductive semiconductor 8 may become 0.2μm. Subsequently, the superconductor is heated in an oxygen atmosphereat 950° C. for 2 hours. Then, the superconducting device of the presentinvention is fabricated.

In this device, the direction in which the maximum superconductingcurrent across superconducting electrodes 3a and 3b flows agrees withthe direction of the flows of currents along the superconductingelectrode 3a--photoconductive semiconductor 8--superconducting electrode3b. Therefore, when light 10 is projected on the photoconductivesemiconductor 8, a great current can be caused to flow. Accordingly, thevalue of the current to flow can be readily controlled with the light,and the device operates as a photodetective device of high sensitivityand high speed.

[Embodiment 13]

There will now be described an embodiment in which a superconductingoxide material having the modified structure of the perovskite typecrystalline structure, including Ba--Y--Cu oxides, is used as thematerial of electrodes and the material of a weak-link portion. In theelectrode portions, the superconducting oxide material is so orientedthat the c-axis of the crystal thereof is perpendicular to the surfaceof the film thereof. The weak-link portion is perpendicular to thedirection of the flow of current, and is in the shape of a band having awidth within 10 μm. In this weak-link portion, the superconducting oxidematerial has such a structure that the c-axis of the crystal thereof isin the direction of the film surface. As an alternative structure, thesuperconducting oxide material in the weak-link portion is made of apolycrystal, the crystal orientations of which are in all directions.

This structure is formed by a method explained below. The single crystalof SrTiO₃, for example, is employed as the material of a substrate. The(100) plane of the SrTiO₃ crystal is set parallel to the surface of thesubstrate. The Ba--Y--Cu oxide, for example, is grown on the substratesurface, whereby the c-axis of the crystal is controlled so as to be ina direction perpendicular to the substrate surface. As regards theweak-link portion, a polycrystalline thin film having ununiform crystalorientations is formed in a part corresponding to the weak-link portion.A Ba--Y--Cu oxide film which is formed on the polycrystalline thin film,becomes a film structure which is polycrystalline and all he crystalorientations (oriented polycrystalline film) of which are not in thec-axial direction.

In order to increase a current capacity in the electrode portions, thesuperconducting oxide film structure of the electrode portions is set ata structure which is made of one crystal in the direction of the flow ofcurrent and in which the crystal is divided by a crystal grain boundaryor twin boundary at a spacing of or below 5 μm vertically to the currentflow direction within the film surface corresponding to the weak-linkportion. In order to obtain such a structure, the parts of the substratecrystal corresponding to the electrode portions of the superconductingoxide film are previously formed with linear defects by dry etching orthe like method.

The superconducting weak-link device operates peculiarly as follows: Ina process for fabricating the superconducting weak-link device, the stepof forming a pattern for the superconducting oxide film itself is notincluded at all. Accordingly, the deterioration of the superconductingcharacteristics of the superconducting oxide film at the stage of thefabrication of the device is out of the question.

Next, the principle of the superconducting weak-link device will bedescribed. The Ba--Y--Cu oxide superconductor will be taken as anexample. As shown in FIG. 14, the crystalline structure of the Ba--Y--Cuoxide is the modified structure of the perovskite crystalline structureand contains the periodic vacancies of oxygen atoms. Referring to thefigure, in planes formed by the a-axis and the b-axis with a Ba atom 23held therebetween, the 3d electrons of Cu atoms 21 and the 2p electronsof oxygen atoms 22 bond to construct bonding pairs. Superconductingelectron pairs flow along the bonding pairs of the Cu atoms 21 and theoxygen atoms 22. The bonding pairs of the Cu atoms 21 and the oxygenatoms 22 do not continuously join in the direction of the c-axis, butthey are severed in the a-b planes holding a Y atom 24 therebetween.Accordingly, the superconducting electrons are easy of flowing in adirection within the a-b plane and are difficult of flowing in thec-axial direction. As a result, superconducting characteristics such asa critical current density are more excellent in the direction withinthe a-b plane than in the c-axial direction. By way of example, acritical magnetic field in the case of applying a magnetic fieldvertically to the c-axis is 3 times as great as a critical magneticfield in the case of applying a magnetic field in parallel with thec-axis. Likewise, the critical current density in the direction withinthe a-b plane is 3 times or more greater than the critical currentdensity in the c-axial direction. Accordingly, electrode portions aremade of a single crystal or a polycrystal the c-axis of the crystal ofwhich is perpendicular to the surface of a substrate, and a weak-linkportion is made of a polycrystal the c-axis of the crystal of which doesnot become perpendicular to the substrate surface. With such astructure, the critical current of the weak-link portion becomes lowerthan that of the electrode film portions. Accordingly, when current iscaused to flow through the device, the shift of a superconductingelectron wave phase arises in the weak-link portion, and characteristicsas a Josephson device are exhibited.

The controls of the crystal orientations as stated above can beperformed by selecting subbing materials. By way of example, SrTiO₃ hasthe perovskite type crystalline structure of cubic system and has alattice constant of 0.3905 nm. On the other hand, the Ba--Y--Cu oxidehas an orthorhombic structure, the lattice constants of which area=0.3894 nm, b=0.3820 nm and c=1.1688 nm. Thus, the lattice constant ofSrTiO₃ is nearly equal to the a-axial and b-axial lattice constants ofthe Ba--Y--Cu oxide. Both SrTiO₃ and the Ba--Y--Cu oxide have thecrystalline structures belonging to the perovskite type, and have nearlyequal atomic spacings. Therefore, the crystal orientation of theBa--Y--Cu oxide film can be controlled by forming the Ba--Y--Cu oxide onthe subbing material of SrTiO₃. In order to prevent the Ba--Y--Cu oxidecrystal from being so oriented that the c-axis becomes perpendicular tothe subbing material, a polycrystalline insulator film or amorphousinsulator film the crystal orientations of which are not fixed isemployed as the subbing material.

An effect to be stated below is produced by the fact that thesuperconducting oxide film structure of the electrode portions is set atthe structure which is made of one crystal in the direction of the flowof current and in which the crystal is divided by a grain boundary ortwin boundary at a spacing of or below 5 μm vertically to the currentflow direction within the surface of the film corresponding to theweak-link portion. The coherence length of the Ba--Y--Cu oxide for thesuperconducting electrons is 1 nm. Accordingly, it incurs the loweringof the current capacity that the grain boundary attended with thevariation of a composition exists in the direction of the flow of thecurrent. Meanwhile, when it is intended to attain a current capacity ofat least 10⁴ A/cm², vortices develop with a conduction current. Unlessthe vortices generated in the electrodes are pinned, a voltage isgenerated by a vortex flow, and the superconducting state is broken. Thegrain boundary or twin boundary is formed vertically to the direction ofthe current conduction, and is assigned the role of a pinning center forfixing the vortices in the electrode regions.

Referring now to FIG. 15, the thirteenth embodiment of the presentinvention will be described. The fundamental structure of a devicehaving weak link with oxide superconductors consists of a substratematerial 1, superconducting electrodes 3a and 3b and a weak-link portion9. Single-crystal SrTiO₃ is employed as the substrate material. Thematerial of the superconducting electrodes is a Ba--Y--Cu oxide, thecomposition ratio of which among B, Y and Cu is set at 2:1:3. On theother hand, the composition ratio value of oxygen is between 6 and 7.The single crystal of SrTiO₃ as the substrate material is in the statein which the surface of the substrate is oriented in the (100) plane.Amorphous Al₂ O₃ 13 is formed on a substrate part which corresponds tothe weak-link portion of the oxide superconducting weak-link device.

A process for manufacturing the oxide superconducting weak-link deviceis as follows: A resist pattern having a width of 0.8 μm and intervalsof 1 μm is formed on an SrTiO₃ single-crystal substrate 1. The exposedpart of the SrTiO₃ substrate 1 is etched by ion-beam etching with Ar.The depth of an etched recess 14 is about 10 nm. Subsequently, analumina film 13 having a thickness of 30 nm is formed by electron-beamevaporation. In order to prevent the defects or omission of oxygenatoms, the formation of the alumina film 13 is carried out in anatmosphere of oxygen gas. A resist pattern is previously formed on thepart other than a weak-link portion so as to prevent the formation ofthe alumina film. The temperature of the substrate during theevaporation is the room temperature. Single-crystal alumina (sapphire)is used as an evaporation source. The structure of the alumina filmformed under such conditions was amorphous according to the result of anX-ray diffraction measurement.

On the substrate 1 processed as described above, a Ba--Y--Cu oxide filmis formed. The Ba--Y--Cu oxide film is formed by rf-magnetron sputteringwith a Ba--Y--Cu oxide target. The substrate temperature during theformation of the film is set at or below 400° C. The thickness of thefilm is 1 μm. After the formation thereof, the Ba--Y--Cu oxide film isheat-treated within a range of 800° C.-1000° C. in an oxygen atmosphere,thereby to be crystallized. The result of an X-ray diffractionmeasurement has revealed that the crystalline structure of the Ba--Y--Cuoxide formed on an SrTiO₃ substrate 5 under the same conditions is themodified structure of the perovskite type crystal as shown in FIG. 14and exhibits the orientation in which the c-axis thereof isperpendicular to the surface of the oxide film. In addition, thecrystalline structure of the Ba--Y--Cu oxide formed on an aluminasubstrate under the same conditions had the modified structure of theperovskite crystal as shown in FIG. 14, but the crystal did not exhibitany special orientation. According to the result of an observation witha scanning electron microscope, the Ba--Y--Cu oxide in the electrodeportions 3a and 3b had a linear crystal shape in correspondence with theetching pattern of the substrate, and almost no grain boundaries existedin the linear parts.

The characteristics of the device having weak ling with the Ba--Y--Cuoxide superconductors as fabricated in the above way were measured.Then, the critical current of the device changed at periods of severaloersted. This indicates that the device having the weak link with theBa--Y--Cu oxide superconductors has the Josephson effect. Further, ithas been verified that the critical current of the device amounts to 100μA even at the liquid nitrogen temperature, and that the Josephsoneffect is exhibited in the magnetic field dependence of the criticalcurrent, etc.

The critical current density of the electrode film portions at theliquid nitrogen temperature was at least 10⁷ A/cm², and exceeded 100times that of the weak-link portion. In contrast, when a Ba--Y--Cu oxidefilm was formed using as a subbing material an SrTiO₃ single-crystalsubstrate which was not subjected to the etching process, the criticalcurrent density thereof at the liquid nitrogen temperature was at most10⁶ A/cm².

As thus far described, according to the present embodiment, thefollowing effects are attained as to superconducting devices:

(1) The superconducting critical temperature of a Ba--Y--Cu oxide is 90K or higher, and the operation of a superconducting device at the liquidnitrogen temperature has become possible.

(2) Since there is no processing step after the formation of a Ba--Y--Cuoxide film, the superconducting characteristics of the Ba--Y--Cu oxidefilm do not deteriorate.

(3) Owing to an electrode film structure which pins vortices, thecritical current density of the electrode film heightens as comparedwith that of a Ba--Y--Cu oxide film in the prior art.

As shown in FIG. 16, a photoconductive semiconductor 16 made of CdS andhaving a thickness of about 3 μm was formed on a superconducting devicehaving the same construction as in FIG. 15. When light was projected onthe photoconductive semiconductor, a superconducting weak-linkphotodetective device the superconducting current of which was decreasedby the incident light could be realized.

(La₀.9 Ca₀.1)₂ CuO₄ was employed as the semiconductor material of theforegoing embodiments. This utilizes the feature that, in a materialwhose composition is denoted by (La_(1-x) A_(x))₂ CuO₄ where A indicatesSr_(1-y-z) Ba_(y) Ca_(z), by changing the value x, y or z, thesuperconducting critical temperature of the material can be changed inthe state in which the crystallographic properties of the material areheld constant. That is, the superconducting material is turned into asemiconductor or a normal-conductor by changing the composition thereof.Even in cases where, as the semiconductor or normal-conductor, theceramics material was replaced with any of metals such as Cu, Au, Ni andSn or any of semiconductors such as Si, Ge, GaAs, InSb, InP and InAs,similar effects could be attained.

Besides, although SrTiO₃ was employed as the substrate material, any ofMgO, sapphire and a garnet material such as GGG may well be employed.Although CdS was employed as the photoconductive material, it may wellbe replaced with any of Si, InP, InAs, InSb and GaAs.

In the foregoing embodiments, (La₀.9 Sr₀.1)₂ CuO₄ was employed as thesuperconducting material. Needless to say, however, even when it isreplaced with a superconducting oxide material having a composition ofYBa₂ Cu₃ O₇₋δ, the objects of the present invention can besatisfactorily accomplished. In this material, Y may well be substitutedby any of La, Yb, Lu, Tm, Dy, Sc, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Ho, Er,etc., and similar effects can be attained. Such examples are listed inTable 1:

                  TABLE 1                                                         ______________________________________                                        Semiconductor                                                                   (Normal-conductor) Superconductor                                           ______________________________________                                        EuBa.sub.2 Cu.sub.3 O.sub.7-y                                                             y > 0.5  EuBa.sub.2 Cu.sub.3 O.sub.7-y                                                               0 < y < 0.5                                  EuSr.sub.2 Cu.sub.3 O.sub.7-y          y > 0.5     EuSr.sub.2 Cu.sub.3                                         O.sub.7-y     0 < y < 0.5                    HoBa.sub.2 Cu.sub.3 O.sub.7-y          y > 0.5     HoBa.sub.2 Cu.sub.3                                         O.sub.7-y     0 < y < 0.5                    HoSr.sub.2 Cu.sub.3 O.sub.7-y          y > 0.5     HoSr.sub.2 Cu.sub.3                                         O.sub.7-y     0 < y < 0.5                    GdBa.sub.2 Cu.sub.3 O.sub.7-y          y > 0.5     GdBa.sub.2 Cu.sub.3                                         O.sub.7-y     0 < y < 0.5                    GdSr.sub.2 Cu.sub.3 O.sub.7-y          y > 0.5     GdSr.sub.2 Cu.sub.3                                         O.sub.7-y     0 < y < 0.5                    YbBa.sub.2 Cu.sub.3 O.sub.7-y          y > 0.5     YbBa.sub.2 Cu.sub.3                                         O.sub.7-y     0 < y < 0.5                    YbSr.sub.2 Cu.sub.3 O.sub.7-y          y > 0.5     YbSr.sub.2 Cu.sub.3                                         O.sub.7-y     0 < y < 0.5                    TbBa.sub.2 Cu.sub.3 O.sub.7-y          y > 0.5     TbBa.sub.2 Cu.sub.3                                         O.sub.7-y     0 < y < 0.5                    TbSr.sub.2 Cu.sub.3 O.sub.7-y          y > 0.5     TbSr.sub.2 Cu.sub.3                                         O.sub.7-y     0 < y < 0.5                    NdCa.sub.2 Cu.sub.3 O.sub.7-y          y > 0.5     NdCa.sub.2 Cu.sub.3                                         O.sub.7-y     0 < y < 0.5                    NdSr.sub.2 Cu.sub.3 O.sub.7-y          y > 0.5     NdSr.sub.2 Cu.sub.3                                         O.sub.7-y     0 < y < 0.5                    SmBa.sub.2 Cu.sub.3 O.sub.7-y          y > 0.5     SmBa.sub.2 Cu.sub.3                                         O.sub.7-y     0 < y < 0.5                    SmSr.sub.2 Cu.sub.3 O.sub.7-y          y > 0.5     SmSr.sub.2 Cu.sub.3                                         O.sub.7-y     0 < y < 0.5                    Ba.sub.2x La.sub.2(1-x) CuO.sub.4(1-y)  x > 0.05    Ba.sub.2x La.sub.2(1                                       -x) CuO.sub.4(1-y)  x = 0.05                 Sr.sub.2x La.sub.2(1-x) CuO.sub.4(1-y)  x > 0.05    Sr.sub.2x La.sub.2(1                                       -x) CuO.sub.4(1-y)  x = 0.05                 Ca.sub.2x La.sub.2(1-x) CuO.sub.4(1-y)  x > 0.05    Ca.sub.2x La.sub.2(1                                       -x) CuO.sub.4(1-y)  x = 0.05                 Ba.sub.2x Y.sub.2(1-x) CuO.sub.4(1-y)   x > 0.05    Ba.sub.2x Y.sub.2(1-                                       x) CuO.sub.4(1-y)   x = 0.05                 Sr.sub.2x Y.sub.2(1-x) CuO.sub.4(1-y)   x > 0.05    Sr.sub.2x Y.sub.2(1-                                       x) CuO.sub.4(1-y)   x = 0.05                 Ba.sub.2x Eu.sub.2(1-x) CuO.sub.4(1-y)  x > 0.05    Ba.sub.2x Eu.sub.2(1                                       -x) CuO.sub.4(1-y)  x = 0.05                 Sr.sub.2x Eu.sub.2(1-x) CuO.sub.4(1-y)  x > 0.05    Sr.sub.2x Eu.sub.2(1                                       -x) CuO.sub.4(1-y)  x = 0.05                 Ba.sub.2x Eu.sub.2(1-x) CuO.sub.4(1-y)  x > 0.05    Ba.sub.2x Eu.sub.2(1                                       -x) CuO.sub.4(1-y)  x = 0.05               ______________________________________                                    

We have shown various above-mentioned embodiments. The present inventionis summaried as follows:

(1) A superconducting device comprising:

a substrate;

at least one superconductor which is formed on said substrate, and whichproperty depends upon the crystallographic orientation in such a mannerthat a superconductivity of the superconducting material constitutingsaid superconductor within a plane is intense, a direction in whichcurrent flows through said superconductor being agreement with adirection in which said superconductivity is high.

(2) A superconducting device comprising:

a substrate;

at least one superconductor which is formed on said substrate, and whichproperty depends upon the crystallographic orientation in such a mannerthat a superconductivity of the superconducting material constitutingsaid superconductor within a plane perpendicular to the c-axis of acrystal of said superconductor is intense, a direction in which currentflows through said superconductor being agreement with a direction inwhich said superconductivity is high, wherein said superconductorincludes at a part thereof a weak-link portion in which said c-axis of acrystal thereof is not substantially perpendicular to said direction ofsaid current flowing through said superconductor.

(3) a superconducting device comprising:

either of a semiconductor body and a normal-conductor body;

and at least two superconductors which are formed in contact with saideither of said semiconductor body and said normal-conductor body, whichproperty depends upon the crystallographic orientation in such a mannerthat a superconductivity of the superconducting material constitutingsaid superconductors within a plane perpendicular to the c-axis of acrystal of said superconductors is intense, which are spaced from eachother so as to form superconducting weak-link through said either ofsaid semiconductor body and said normal-conductor body, said c-axisbeing substantially perpendicular to a direction of current flowingthrough said superconductors, said plane of said crystal of saidsuperconductors is substantioally perpendicular to a contact planebetween said either of said semiconductor body and said normal-conductorbody and said superconductors in said superconducting weak-link.

What is claimed is:
 1. A superconducting device comprising:asuperconductor, formed of a high Tc superconducting oxide having acrystalline structure, substantially all of the crystals of said high Tcsuperconducting oxide having a c-axis oriented in the same direction andincluding at a part thereof a weak-link portion; electrodes forachieving a superconducting current flow through the superconductor sothat the c-axis of the crystals is substantially perpendicular to adirection of the current flowing therethrough.
 2. A superconductingdevice according to claim 1, wherein the crystalline structure of thehigh Tc superconducting oxide is selected from the group consisting ofperovskite crystalline structure and K₂ NiF₄ crystalline structure.
 3. Asuperconducting device according to claim 1, further comprising aphotoconductive semiconductor adjacent said weak-link portion.
 4. Asuperconducting device according to claim 3, wherein the photoconductivesemiconductor is Cds.
 5. A superconducting device according to claim 3,wherein said photoconductive semiconductor is on said weak-link portion.6. A superconducting device according to claim 3, wherein thesuperconductor is provided on a substrate, said substrate being made ofsaid photoconductive semiconductor.
 7. A superconducting deviceaccording to claim 6, wherein said substrate has a projection, of saidphotoconductive semiconductor, at said weak-link portion.
 8. Asuperconducting device according to claim 7, wherein an upper surface ofsaid superconductor is uniform.
 9. A superconducting device according toclaim 3, wherein the superconductor is provided on a substrate, and,adjacent the weak-link portion, between the superconductor and thesubstrate, is provided the photoconductive semiconductor.
 10. Asuperconducting device according to claim 9, where in an upper surfaceof said superconductor is uniform.
 11. A superconducting deviceaccording to claim 1, where in the superconductor is provided on asubstrate, and the c-axis of the crystals is perpendicular to thesubstrate.